KR102531436B1 - Ammonia slip catalyst with low N2O formation - Google Patents

Abstract

Catalysts with blends of platinum on supports and SCR catalysts with low ammonia storage are disclosed. The catalyst may also contain one or two additional SCR catalysts. Catalysts can be present in one of a variety of configurations. Catalyst articles containing these catalysts are disclosed. Catalytic articles are useful for selective catalytic reduction (SCR) of NOx in exhaust gases and reducing the amount of ammonia slip. Methods of producing such articles are disclosed. A method of using the catalytic article in an SCR process in which the amount of ammonia slip is reduced is also disclosed.

Description

Ammonia slip catalyst with low N2O formation

The present invention relates to an ammonia slip catalyst (ASC), an article containing the ammonia slip catalyst and a method of making and using the article to reduce ammonia slip.

Combustion of hydrocarbons in diesel engines, stationary gas turbines, and other systems generates exhaust gases that must be treated to remove nitrogen oxides (NOx), including NO (nitrogen oxide) and NO ₂ (nitrogen dioxide), and NOx formed. Most of are NO. NOx is known to cause many harmful environmental effects, including smog formation and acid rain, as well as causing many human health problems. In order to mitigate both the human and environmental impact of NO _x in exhaust gas, it is desirable to remove these unwanted components, preferably by processes that do not generate other toxic or toxic substances.

Exhaust gases from lean-burn and diesel engines are generally oxidizing. NOx needs to be reduced selectively with a catalyst and a reducing agent in a process known as selective catalytic reduction (SCR) which converts NOx to elemental nitrogen (N ₂ ) and water. In the SCR process, a gaseous reducing agent, typically anhydrous ammonia, aqueous ammonia, or urea, is added to the exhaust gas stream before the exhaust gas contacts the catalyst. The reducing agent is absorbed into the catalyst and NO _x is reduced as the gas passes through or on the catalyzed substrate. To maximize NOx conversion, it is often necessary to add more than a stoichiometric amount of ammonia to the gas stream. However, the release of excess ammonia into the atmosphere would be detrimental to human health and the environment. In addition to this, ammonia is caustic, especially in aqueous form. Condensation of ammonia and water in the area of the exhaust line downstream of the exhaust catalyst can generate a corrosive mixture that can damage the exhaust system. Therefore, the emission of ammonia in the exhaust gas must be eliminated. In many conventional exhaust systems, an ammonia oxidation catalyst (also known as an ammonia slip catalyst or "ASC") is installed downstream of the SCR catalyst to remove ammonia from the exhaust gas by converting the ammonia to nitrogen. The use of an ammonia slip catalyst can allow greater than 90% NO _x conversion over a typical diesel drive cycle.

It is desirable to have a catalyst that provides NOx removal by SCR and selective conversion of ammonia to nitrogen, wherein ammonia conversion occurs over a wide range of temperatures in the vehicle's drive cycle, with minimal formation of nitric oxide and nitrous oxide by-products.

In a first aspect, the invention relates to a catalyst comprising a combination of platinum on a support with low ammonia storage and a first SCR catalyst, preferably a Cu-SCR catalyst or a Fe-SCR catalyst. Supports with low ammonia storage may be siliceous supports. The siliceous support may comprise silica or a zeolite having a silica to alumina ratio of at least 100. The combination of platinum on a support with low ammonia storage is (1) a blend of platinum on a support with low ammonia storage and the first SCR catalyst, or (2) a top layer comprising the first SCR catalyst and a low It is a double layer having a lower layer comprising platinum on a support with ammonia storage, the lower layer being located on the substrate or a third SCR catalyst located between the lower layer and the third SCR catalyst. The catalyst may further comprise a second SCR catalyst, the second SCR catalyst positioned adjacent to the blend of platinum and the first SCR catalyst on a low ammonia storage support and the second SCR catalyst comprising a low ammonia storage support. At least partially overlaps with the blend of the platinum phase and the first SCR. The catalyst may further comprise a third SCR catalyst, wherein the third SCR catalyst is positioned adjacent to the blend of the platinum on support having low ammonia storage and the first SCR catalyst, and the third SCR catalyst is positioned adjacent to the blend of the platinum on support having low ammonia storage and the second SCR catalyst. The blend of one SCR catalyst at least partially overlaps the third SCR catalyst. The catalyst comprises a comparative formulation in which the first SCR catalyst is present as a first layer and the supported platinum is present in a second layer and a gas comprising NH ₃ is passed through the first layer before passing through the second layer. It can provide an improvement in N ₂ yield from ammonia at temperatures from about 250° C. to about 350° C. as compared to catalysts.

In another aspect, the present invention relates to a method for preparing a catalyst comprising a blend of platinum on a support with low ammonia storage and a first SCR catalyst, the first SCR catalyst being preferably a Cu-SCR catalyst or Fe -SCR catalyst.

In another aspect, the present invention provides an article comprising a catalyst comprising a blend of platinum on a support and a first SCR catalyst having low ammonia storage, and an improved N ₂ yield from ammonia at a temperature of about 250 °C to about 350 °C. wherein the first SCR catalyst is preferably a Cu-SCR catalyst or a Fe-SCR catalyst.

In another aspect, the present invention relates to an exhaust system comprising a catalyst comprising a blend of platinum on a support and a first SCR catalyst having low ammonia storage, and articles containing these catalysts, wherein the first SCR catalyst is preferably Preferably it is a Cu-SCR catalyst or a Fe-SCR catalyst.

In another aspect, the present invention relates to an exhaust gas comprising ammonia by contacting a catalyst comprising a blend of platinum and a first SCR catalyst on a support having a low ammonia storage, thereby reducing in the exhaust gas at a temperature of about 250 °C to about 350 °C. It relates to a method for improving N ₂ yield from ammonia, wherein the first SCR catalyst is preferably a Cu-SCR catalyst or a Fe-SCR catalyst.

In yet another aspect, the present invention relates to a method for reducing N ₂ O formation from NH ₃ in an exhaust gas, the method comprising mixing an exhaust gas containing ammonia and a first SCR catalyst with platinum on a support having low ammonia storage. contacting a catalyst comprising the blend, wherein the first SCR catalyst is preferably a Cu-SCR catalyst or a Fe-SCR catalyst.

Figures 1-7 are schematic diagrams of a batch of catalysts comprising a blend of a first SCR catalyst with platinum on a support having low ammonia storage. Some of the catalysts, including blends of platinum on supports with low ammonia storage and the first SCR catalyst, are labeled "blends" in these figures.
1 shows an arrangement in which the second SCR is positioned above the blend in the exhaust stream and the second SCR covers the entire blend.
Figure 2 shows an arrangement in which the second SCR is positioned in front of the blend in the exhaust stream and the second SCR covers the entire blend.
Figure 3 shows an arrangement where the second SCR is positioned before the blend in the exhaust stream and the second SCR covers a portion of the blend, but not the entire blend.
Figure 4 shows an arrangement where the second SCR covers the entire blend and a portion of the second SCR is located behind the blend in the exhaust gas flow.
5 shows an arrangement where the second SCR covers part of the blend, but not the entire blend, and a part of the second SCR is located behind the blend in the exhaust gas flow.
6 shows that the third SCR catalyst is a lower layer on the substrate, the second layer comprises the blend and partially covers the third SCR catalyst, the third layer comprises the second SCR and is located above the second layer; Shows a layout covering all of the blend layers.
7 shows a third SCR catalyst as a lower layer on the substrate, the second layer comprising the blend and covering partially, but not completely, the third SCR catalyst, the third layer comprising the second SCR, and It is located above, and shows an arrangement that partially, but not completely, covers all of the blend layers.
Figure 8 shows a batch with a single layer containing blends.
9-11 show an arrangement in which platinum on support with low ammonia storage is present in a layer and the layer does not contain a blend of platinum on siliceous support in the first SCR catalyst. Some of the catalysts, including blends of platinum on supports with low ammonia storage and the first SCR catalyst, are labeled "supported Pt" in these figures.
Figure 9 shows an arrangement in which the second SCR is positioned above the supported layer of platinum in the exhaust gas stream and the second SCR covers the entire layer of supported platinum.
FIG. 10 shows an arrangement in which the second SCR is positioned in front of the blend in the exhaust stream and the second SCR covers the entire layer of supported platinum.
11 shows a third SCR in a lower layer on the substrate, the second layer comprising a supported layer of platinum and partially covering the third SCR catalyst, the third layer comprising the second SCR, and It shows an arrangement covering the entire layer of platinum placed on top and supported.

As used in this specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a catalyst” includes mixtures of two or more catalysts, and the like.

As used herein, the term “ammonia slip” refers to the amount of unreacted ammonia that passes through the SCR catalyst.

The term "support" means a material to which a catalyst is immobilized.

The term “support with low ammonia storage” means a support that stores less than 0.001 mmol NH ₃ per m ³ of support. Supports with low ammonia storage are preferably AEI, ANA, ATS, BEA, CDO, CFI, CHA, CON, DDR, ERI, FAU, FER, GON, IFR, IFW, IFY, IHW, IMF, IRN, IRY , ISV, ITE, ITG, ITN, ITR, ITW, IWR, IWS, IWV, IWW, JOZ, LTA, LTF, MEL, MEP, MFI, MRE, MSE, MTF, MTN, MTT, MTW, MVY, MWW, NON , NSI, RRO, RSN, RTE, RTH, RUT, RWR, SEW, SFE, SFF, SFG, SFH, SFN, SFS, SFV, SGT, SOD, SSF, SSO, SSY, STF, STO, STT, SVR, SVV , TON, TUN, UOS, UOV, UTL, UWY, VET, VNI. More preferably, the support with low ammonia storage is a molecular sieve or zeolite having a framework type selected from the group consisting of BEA, CDO, CON, FAU, MEL, MFI and MWW, more preferably the framework type is It is selected from the group consisting of BEA and MFI.

The term "calcinate" or "calcining" means heating a material in air or oxygen. This definition is consistent with the IUPAC definition of calcining. (IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Edited by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). M. Nic, J. Jirat, B. Kosata XML online corrected version generated by: http://goldbook.iupac.org (2006-); updated edited by A. Jenkins, ISBN 0-9678550-9-8. doi:10.1351/ goldbook). Calcination is performed to decompose the metal salt to promote the exchange of metal ions in the catalyst and to adhere the catalyst to the substrate. The temperature used for calcination depends on the composition of the material being calcined and is generally from about 400° C. to about 900° C. for approximately 1 to 8 hours. In some cases, calcination may be conducted at temperatures up to about 1200 °C. In applications involving the processes described herein, calcination is generally performed at a temperature of about 400° C. to about 700° C. for about 1 to 8 hours, preferably at a temperature of about 400° C. to about 650° C. for about 1 to 4 hours. is performed in

The term "about" means approximately and optionally refers to a range that is ± 25%, preferably ± 10%, more preferably ± 5%, or most preferably ± 1% of the value associated with the term.

When a range or ranges are provided for various numerical elements, the range or ranges may include values unless otherwise specified.

The term “N ₂ selectivity” refers to the percent conversion of ammonia to nitrogen.

In a first aspect of the present invention, the catalyst comprises a combination of platinum on a support with low ammonia storage and a first SCR catalyst. The combination of platinum on a support with low ammonia storage and the first SCR catalyst may be (a) a blend of platinum on a support with low ammonia storage and the first SCR catalyst, or (b) a top layer comprising the first SCR catalyst. and a lower layer comprising platinum on a support having low ammonia storage, the lower layer being positioned on the substrate. Supports with low ammonia storage may be siliceous supports. The siliceous support is silica or ≥ 100, preferably ≥ 200, more preferably ≥ 250, more preferably ≥ 300, particularly ≥ 400, more particularly ≥ 500, more particularly ≥ 750, and most preferably ≥ 1000 It may include a zeolite having a ratio of silica to alumina of In each aspect of the present invention, the first SCR catalyst is preferably a Cu-SCR catalyst or a Fe-SCR catalyst, more preferably a Cu-SCR catalyst.

The ratio of the amount of the first SCR catalyst to the amount of platinum on the support with low ammonia storage in the blend is from 0.1 to 300:1, preferably from 3:1 to 300:1, more preferably from 3:1 to 300:1, based on the weight of these components. preferably in the range of 7:1 to 100:1, more preferably in the range of 10:1 to 50:1.

The term "active component loading" refers to the weight of the carrier of platinum + the weight of platinum + the weight of the first SCR catalyst in the blend. Platinum is about 0.01 to about 0.3 weight percent (wt.%), preferably about 0.03-0.2 weight percent, more preferably about 0.05-0.17 weight percent, most preferably about 0.07-0.15 weight percent active. It may be present in the catalyst as a component loading. When platinum is present in the bottom layer of the bilayer, platinum may be present at about 0.1% to 2%, preferably 0.1 to 1%, more preferably 0.1% to 0.5% by weight relative to the weight of the layer. Additional catalysts such as palladium (Pd), gold (Au), silver (Ag), ruthenium (Ru) or rhodium (Rh) may be present together with Pt, preferably in admixture with Pt.

SCR Catalyst

In various embodiments, the composition may include one, two or three SCR catalysts. The first SCR catalyst always present in the composition can be (1) mixed with Pt on a support having low ammonia storage or (2) in the top layer when the catalyst is in the bilayer and Pt is in the bottom layer. The first SCR catalyst is preferably a Cu-SCR catalyst or a Fe-SCR catalyst, more preferably a Cu-SCR catalyst. Cu-SCR catalysts include copper and molecular sieves. Fe-SCR catalysts include iron and molecular sieves. Molecular sieves are described further below. The molecular sieve can be an aluminosilicate, aluminophosphate (AlPO), silico-aluminophosphate (SAPO), or a mixture thereof. The copper or iron may be located within the framework of the molecular sieve and/or at extra framework (exchangeable) sites within the molecular sieve.

The second and third SCR catalysts may be the same or different. The second and third SCR catalysts may be a base metal, an oxide of a base metal, a noble metal, a molecular sieve, a metal exchange molecular sieve, or a mixture thereof. Nonmetals include vanadium (V), molybdenum (Mo), tungsten (W), chromium (Cr), cerium (Ce), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and copper ( Cu), and mixtures thereof. SCR compositions composed of vanadium supported on refractory metal oxides such as alumina, silica, zirconia, titania, ceria and combinations thereof are well known and widely used commercially in mobile applications. Exemplary compositions are described in US Pat. Nos. 4,010,238 and 4,085,193, which are incorporated herein by reference in their entirety. Compositions used commercially, particularly in mobile applications, include TiO ₂ dispersed in concentrations ranging from 5 to 20% by weight and 0.5 to 6% by weight of WO ₃ and V ₂ O ₅ , respectively. The noble metal may be platinum (Pt), palladium (Pd), gold (Au) silver (Ag), ruthenium (Ru) or rhodium (Rh), or mixtures thereof. The second SCR catalyst may include promoted Ce-Zr or MnO ₂ . These catalysts may also contain other inorganic materials, such as SiO ₂ and ZrO ₂ , which act as binders and promoters.

When the SCR catalyst is a non-metal, the catalyst may further include at least one non-metal promoter. As used herein, “promoter” is understood to mean a substance that, when added to a catalyst, increases the activity of the catalyst. A non-metal promoter may be in the form of a metal, an oxide of a metal, or a combination thereof. The at least one non-metal catalytic promoter is neodymium (Nd), barium (Ba), cerium (Ce), lanthanum (La), praseodymium (Pr), magnesium (Mg), calcium (Ca), manganese (Mn), zinc (Zn) ), niobium (Nb), zirconium (Zr), molybdenum (Mo), tin (Sn), tantalum (Ta), strontium (Sr), and oxides thereof. The at least one non-metal catalyzed promoter is preferably MnO ₂ , Mn ₂ O ₃ , Fe ₂ O ₃ , SnO ₂ , CuO, CoO, CeO ₂ and mixtures thereof. At least one non-metal catalytic promoter may be added to the catalyst in the form of a salt in an aqueous solution, such as nitrate or acetate. At least one non-metal catalyzed promoter and at least one non-metal catalyst, such as copper, may be impregnated with the oxide support material(s) from an aqueous solution, or as a washcoat comprising the oxidizer support material(s). It may be added or it may be impregnated with a support previously coated with a washcoat.

The SCR catalyst may include a molecular sieve or a metal-exchanged molecular sieve. As used herein, "molecular sieve" is understood to mean a metastable material containing very small pores of precise and uniform size, which can be used as an adsorbent for gases or liquids. Molecules too small to pass through the pores are adsorbed, but larger molecules are not. The molecular sieve can be a zeolitic molecular sieve, a non-zeolitic molecular sieve, or a mixture thereof.

A zeolite molecular sieve is a microporous aluminosilicate having any one of the framework structures listed in the Database of Zeolite Structures published by the International Zeolite Association (IZA). Framework structures include, but are not limited to, those of type CHA, FAU, BEA, MFI, and MOR. Non-limiting examples of zeolites having these structures include chabazite, faujasite, zeolite Y, ultrastable zeolite Y, beta zeolite, mordenite, silicalite, zeolite X, and ZSM-5. . Aluminosilicate zeolites can have a silica/alumina molar ratio (SAR; defined as SiO ₂ /Al ₂ O ₃ ) of at least about 5, preferably at least about 20, with a useful range of about 10 to 200.

Any of the SCR catalysts may include small, meso or large pore molecular sieves, or mixtures thereof. A “small pore molecular sieve” is a molecular sieve containing tetrahedral atoms of a maximum ring size of 8. "Mesopore molecular sieve" is a molecular sieve containing tetrahedral atoms of a maximum ring size of 10. A “large-pore molecular sieve” is a molecular sieve containing tetrahedral atoms of a maximum ring size of 12. The second and/or third SCR catalyst may be an aluminosilicate molecular sieve, a metal-substituted aluminosilicate molecular sieve, an aluminophosphate (AlPO) molecular sieve, a metal-substituted aluminophosphate (MeAlPO) molecular sieve, a silico- small pore molecular sieves selected from the group consisting of aluminophosphate (SAPO) molecular sieves, and metal substituted silico-aluminophosphate (MeSAPO) molecular sieves, and mixtures thereof.

None of the SCR catalysts are ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW , LEV, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SFW, SIV, THO, TSC, UEI, UFI, VNI, YUG, and ZON, and mixtures thereof and/or or a small pore molecular sieve selected from the group of framework types consisting of intergrowth. Preferably the small pore molecular sieve is selected from the group of framework types consisting of CHA, LEV, AEI, AFX, ERI, SFW, KFI, DDR and ITE.

None of the SCR catalysts are AEL, AFO, AHT, BOF, BOZ, CGF, CGS, CHI, DAC, EUO, FER, HEU, IMF, ITH, ITR, JRY, JSR, JST, LAU, LOV, MEL, MFI, MFS , MRE, MTT, MVY, MWW, NAB, NAT, NES, OBW, PAR, PCR, PON, PUN, RRO, RSN, SFF, SFG, STF, STI, STT, STW, -SVR, SZR, TER, TON, mesoporous molecular sieve selected from the group of framework types consisting of TUN, UOS, VSV, WEI, and WEN, and mixtures and/or symbiotics thereof. Preferably, a mesoporous molecular sieve selected from the group of framework types consisting of MFI, FER and STT.

None of the SCR catalysts are AFI, AFR, AFS, AFY, ASV, ATO, ATS, BEA, BEC, BOG, BPH, BSV, CAN, CON, CZP, DFO, EMT, EON, EZT, FAU, GME, GON, IFR , ISV, ITG, IWR, IWS, IWV, IWW, JSR, LTF, LTL, MAZ, MEI, MOR, MOZ, MSE, MTW, NPO, OFF, OKO, OSI, RON, RWY, SAF, SAO, SBE, SBS , SBT, SEW, SFE, SFO, SFS, SFV, SOF, SOS, STO, SSF, SSY, USI, UWY, and VET, and mixtures and/or biomes thereof Molecular sieves may be included. Preferably, the porous molecular sieve is selected from the group of framework types consisting of MOR, OFF and BEA.

The molecular sieve in the Cu-SCR and Fe-SCR catalysts is preferably ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI , GIS, GOO, IHW, ITE, ITW, LEV, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, ZON , BEA, MFI and FER, and mixtures and/or symbionts thereof. More preferably, the molecular sieves in Cu-SCR and Fe-SCR are AEI, AFX, CHA, DDR, ERI, ITE, KFI, LEV, SFW, BEA, MFI and FER, and mixtures and/or epizoites thereof selected from the group consisting of

The metal exchanged molecular sieve is any of group VB, VIB, VIIB, VIIIB, IB, or IIB of the periodic table, deposited in extra framework sites on the outer surface of the molecular sieve or within channels, cavities, or cages of the molecular sieve. It can have at least one metal. The metal may be in one of several forms including, but not limited to, zero-valent metal atoms or clusters, isolated cations, mononuclear or polynuclear oxygenations, or may exist as extended metal oxides. Preferably, the metal may be iron, copper, and mixtures or combinations thereof.

Iron can be combined with the zeolite using a mixture or solution of the metal precursor in a suitable solvent. The term “metal precursor” means any compound or complex that can be dispersed on a zeolite to provide a catalytically active metal component. The solvent is preferably water due to both the economic and environmental aspects of using other solvents. When the preferred metal, copper, is used, suitable complexes or compounds include anhydrous and hydrated copper sulfate, copper nitrate, copper acetate, copper acetylacetonate, copper oxide, copper hydroxide, and copper amine salts (e.g., [Cu( NH ₃ ) ₄ ] ²⁺ ), but are not limited thereto. The present invention is not limited to a particular type, composition, or purity of metal precursor. The molecular sieve can be added to a solution of the metal component to form a suspension, which can then be reacted to distribute the metal component onto the zeolite. The metal can be distributed in the pore channels of the molecular sieve, as well as on the external surface. Metals can be distributed in the form of ions or as metal oxides. For example, copper may be distributed as copper (II) ions, copper (I) ions, or as copper oxide. The molecular sieve containing the metal may be separated from the liquid phase of the suspension, washed and dried. The resulting metal-containing molecular sieve can then be calcined to fix the metal in the molecular sieve. Preferably, the second and third catalysts include a Cu-SCR catalyst containing copper and molecular sieve, a Fe-SCR catalyst containing iron and molecular sieve, a vanadium-based catalyst, promoted Ce-Zr or promoted MnO ₂ . include

The metal-exchanged molecular sieve contains from about 0.10% to about 0.10% by weight of a VB, VIB, VIIB, VIIIB, IB, or Group IIB metal located at extra framework sites on the outer surface of the molecular sieve or within channels, cavities, or cages of the molecular sieve. It may be contained in the range of 10% by weight. Preferably, the extra framework metal may be present in an amount ranging from 0.2% to about 5% by weight.

The metal exchanged molecular sieve can be a copper (Cu) or iron (Fe) supported molecular sieve having from about 0.1 to about 20.0 weight percent copper or iron of the total weight of the catalyst. More preferably copper or iron is present from about 0.5% to about 15% by weight of the total weight of the catalyst. Most preferably copper or iron is present from about 1% to about 9% by weight of the total weight of the catalyst.

The composition may include one or more additional metals in combination with Pt. These one or more additional metals may be gold (Au), iridium (Ir), palladium (Pd), rhodium (Rh), ruthenium (Ru) or silver (Ag). These metals may be present from about 0.1% to about 20% by weight, preferably from about 0.3% to about 10% by weight.

In a first aspect of the invention, the blend of platinum on a support with low ammonia storage and the first SCR catalyst comprises at least one of palladium (Pd), gold (Au) silver (Ag), ruthenium (Ru) or rhodium (Rh). may contain one more.

In a first aspect of the present invention, the lower layer comprising platinum on the support having low ammonia storage further comprises at least one of palladium (Pd), gold (Au) silver (Ag), ruthenium (Ru) or rhodium (Rh). can include The lower layer may also contain a mixed oxide catalyst with ammonia storage. The mixed oxide catalyst is preferably promoted CeZr or MnO ₂ .

The catalysts described herein can be used for SCR treatment of the exhaust gases of a variety of engines. One of the properties of the catalyst comprising a blend of platinum on a support with low ammonia storage and the first SCR catalyst is that, when the first SCR catalyst is a Cu-SCR or Fe-SCR catalyst, the first SCR catalyst is a first layer and platinum supported on a layer storing ammonia is present in a second layer and a gas comprising NH ₃ passes through the first layer before passing through the second layer. This can provide an improvement in N ₂ yield from ammonia at temperatures from about 250 °C to about 350 °C. Another property of the catalyst comprising a blend of platinum on a support with low ammonia storage and the first SCR catalyst is that when the first SCR catalyst is a Cu-SCR catalyst or a Fe-SCR catalyst, the first SCR catalyst is a first SCR catalyst. A catalyst comprising a comparative formulation which is present as a layer and has platinum supported on a support storing ammonia present in the second layer and a gas comprising NH ₃ passes through the first layer before passing through the second layer. can provide a reduction in N ₂ O formation from NH ₃ compared to

In another aspect of the present invention, a method for preparing a catalyst comprising a blend of a first SCR catalyst and platinum on a support having low ammonia storage, wherein the first SCR catalyst is preferably a Cu-SCR catalyst or Fe-SCR In the case of a catalyst, blending a catalyst comprising platinum on a support having low ammonia storage with a first SCR catalyst, wherein the first SCR catalyst is preferably a Cu-SCR catalyst or a Fe-SCR catalyst. One skilled in the art will know how these materials can be blended. For example, platinum is prepared by impregnating a support having a low ammonia storage with a solution of a platinum salt, preferably platinum nitrate, using a conventional incipient wetness technique on a support having a low ammonia storage. It can be. After impregnation, the support may preferably be dried in a static oven at about 100° C. in air for about 5 hours and then calcined in a static oven at about 500° C. in air for 2 hours. Platinum on a support with low ammonia storage can be mixed with the first SCR by various techniques not skilled in the art. For example, a mixture of platinum on a support having low ammonia storage is prepared by slurrying SCR catalyst powder and platinum powder on a support that does not support ammonia using an industrial mixer to obtain a first SCR catalyst and a first SCR catalyst in a washcoat. can be blended. A binder such as alumina may be added. The slurry may then be applied as a washcoat to a substrate, such as a honeycomb substrate.

In one aspect of the present invention, various batches of catalysts can be prepared including blends of a first SCR catalyst with platinum on a support having low ammonia storage. Some of the catalysts comprising a blend of platinum on a support with low ammonia storage in the first SCR catalyst are labeled "blends" in the figures described below.

In the first batch, the catalyst may include a first layer comprising a blend of platinum on a support having low ammonia storage and a first SCR catalyst, and a second layer comprising a second SCR catalyst, wherein the first SCR catalyst is preferably a Cu-SCR catalyst or a Fe-SCR catalyst, and the second layer is located in a layer above the first layer and the second layer covers all of the first layer. 1 shows an arrangement in which the second SCR is positioned above the blend in the exhaust stream and the second SCR covers the entire blend.

In a second arrangement, the catalyst may comprise a first layer comprising a blend of platinum on a support with low ammonia storage and a first SCR catalyst and a second layer comprising a second SCR catalyst, wherein the first SCR catalyst is preferably a Cu-SCR catalyst or an Fe-SCR catalyst, a first portion of the second SCR catalyst is located upstream of the first layer and a second portion of the second SCR catalyst is present in the second layer, covers the entire first layer. Figure 2 shows an arrangement in which the second SCR is positioned in front of the blend in the exhaust gas flow and the second SCR covers the entire blend.

In a third arrangement, the catalyst may comprise a first layer comprising a blend of a first SCR catalyst and platinum on a support having low ammonia storage and a second layer comprising a second SCR catalyst, wherein the first SCR catalyst is preferably a Cu-SCR catalyst or an Fe-SCR catalyst, a first portion of the second SCR catalyst is located upstream of the first layer and a second portion of the second SCR catalyst is present in the second layer, covers part, but not all, of the first layer. The second SCR catalyst may overlap the blend of platinum on a support with low ammonia storage with the first SCR catalyst by an amount of about 10% to 95%, preferably 50% to 95%. FIG. 3 shows an arrangement in which a second SCR is placed in front of the blend in the exhaust stream and the second SCR covers some, but not all, of the blend. In Figure 3, the second SCR covers about 40% of the blend.

In a fourth arrangement, the catalyst may comprise a first layer comprising a blend of a first SCR catalyst and platinum on a support having low ammonia storage, and a second layer comprising a second SCR catalyst, wherein the first SCR catalyst is preferably a Cu-SCR catalyst or an Fe-SCR catalyst, a first portion of the second SCR catalyst is located downstream of the first layer and a second portion of the second SCR catalyst is present in the second layer, and The layer covers all of the first layer. Figure 4 shows an arrangement where the second SCR covers the entire blend and a portion of the second SCR is located behind the blend in the exhaust gas flow.

In a fifth arrangement, the catalyst may comprise a first layer comprising a blend of a first SCR catalyst and platinum on a support having low ammonia storage and a second layer comprising a second SCR catalyst, wherein the first SCR catalyst is preferably a Cu-SCR catalyst or an Fe-SCR catalyst, a first portion of the second SCR catalyst is located downstream of the first layer and a second portion of the second SCR catalyst is present in the second layer, and The layer covers part, but not all, of the first layer. The second SCR catalyst may overlap the blend of platinum on a support with low ammonia storage with the first SCR catalyst by an amount of about 10% to 95%, preferably 50% to 95%. Figure 5 shows an arrangement in which the second SCR covers part of the blend, but not the whole, and part of the second SCR is positioned in the exhaust stream before the blend. In Figure 5, the second SCR covers about 95% of the blend.

In a sixth arrangement, the catalyst may include a first layer comprising a third SCR catalyst. The first layer is partially, but not completely, covered by a blend of platinum on a support with low ammonia storage and a first SCR catalyst, the first SCR catalyst being preferably a Cu-SCR catalyst or a Fe-SCR catalyst. The blend may cover the third SCR catalyst by an amount of about 10% to 95%, preferably 50% to 95%. The second layer is covered by a third layer containing the second SCR catalyst, and the third layer covers the entire second layer. 6 shows a third SCR catalyst is a lower layer on the substrate, a second layer comprising the blend and partially covering the third SCR catalyst, and a third layer comprising the second SCR and located over the second layer and the blend Shows an arrangement covering all of the layers.

In a seventh arrangement, the catalyst may include a first layer comprising a third SCR catalyst. The first layer is partially, but not completely, covered by a blend of platinum on a support with low ammonia storage and a first SCR catalyst, the first SCR catalyst being preferably a Cu-SCR catalyst or a Fe-SCR catalyst. The blend may cover the third SCR catalyst by an amount of about 10% to 95%, preferably 50% to 95%. The second layer is covered by a third layer comprising a second SCR catalyst, the third layer partially but not completely covering the second layer and a portion of the second SCR catalyst located downstream of the blend and also Downstream of the second layer, a part of the third SCR catalyst is covered. The second SCR catalyst may cover the third SCR catalyst by an amount of about 10% to 95%, preferably 50% to 95%. 7 shows a third SCR catalyst as a lower layer on the substrate, the second layer comprising the blend and covering partially, but not completely, the third SCR catalyst, the third layer comprising the second SCR, and It shows an arrangement that is located above and covers partially, but not completely, the blend layer. The second layer covers about 60% of the first layer and the layer having the second SCR covers about 20% of the first layer. The term "covering" means a portion of a layer in direct contact with another layer.

In an eighth arrangement, the catalyst may comprise a single layer comprising platinum on a support with low ammonia storage. Figure 8 shows an arrangement in which a single layer comprising platinum on a support with low ammonia storage is placed in the exhaust stream.

In a ninth arrangement, the catalyst may include a first layer comprising platinum on a support having a low ammonia storage with a first SCR catalyst and a second layer comprising a second SCR catalyst, the second layer comprising a Located on a floor above the first floor, the second floor covers all of the first floor. Figure 9 shows an arrangement in which the second SCR is located above the supported platinum in the exhaust gas flow and the second SCR covers all of the supported platinum.

In a tenth arrangement, the catalyst may comprise a first layer comprising platinum on a support having low ammonia storage and a second layer comprising a second SCR catalyst, wherein a first portion of the second SCR catalyst comprises a first layer comprising A second portion of the second SCR catalyst located upstream of the layer is present in the second layer, the second layer covering all of the first layer. Figure 10 shows an arrangement in which the second SCR is positioned in front of the blend in the exhaust stream and the second SCR covers all of the supported platinum.

In an eleventh arrangement, the catalyst may include a first layer comprising a third SCR catalyst. The first layer is partially, but not completely, covered by a second layer comprising platinum on a support having low ammonia storage. The layer comprising supported platinum may cover the third SCR catalyst by an amount of about 10% to 95%, preferably 50% to 95%. The second layer comprising the supported platinum is covered by a third layer comprising the second SCR catalyst, the third layer covering the entire second layer. 11 shows a third SCR catalyst is a lower layer on the substrate, a second layer comprising supported Pt, partially covering the third SCR catalyst, and a third layer comprising the second SCR and located above the second layer; The arrangement is shown covering all of the supported platinum.

In one aspect of the invention, an article includes (1) the catalyst of the first aspect of the invention, (2) a substrate on which the catalyst is located, (3) an inlet, and (4) an outlet. The catalyst may have one of the configurations described above.

The substrate for the catalyst may be any material typically used to make automotive catalysts, including flow-through or filter structures such as honeycomb structures, extruded supports, metallic substrates, or SCRFs. . Preferably, the substrate has a plurality of fine, parallel gas passages extending from the inlet side to the outlet side of the substrate, thereby opening the passages to fluid flow. Such unitary carriers may contain up to about 700 or more flow passages (or "cells") per square inch of cross section, although far fewer flow passages may be used. For example, the carrier may have from about 7 to about 600 cells per square inch, more usually from about 100 to about 400 cells per square inch ("cpsi"). The passage, which is essentially a straight path from the fluid inlet to the fluid outlet, is defined by walls where the SCR catalyst is coated as a "washcoat" so that the gas passing through the passage comes into contact with the catalyst material. The flow path of the integral substrate is a thin-walled channel that can have any suitable cross-sectional shape, such as trapezoidal, rectangular, square, triangular, sinusoidal, hexagonal, elliptical, circular, and the like. The present invention is not limited to a particular substrate type, material, or geometry.

The ceramic substrate includes cordierite, cordierite-α alumina, α-alumina, silicon carbide, silicon nitride, zirconia, mullite, spodumene, alumina-silica magnesia, zirconium silicate, silimanite, magnesium silicate, zircon, It may be made of any suitable heat resistant material such as petalite, aluminosilicate and mixtures thereof.

Wall flow substrates may also be made of ceramic fiber composite materials, such as those made of cordierite and silicon carbide. These materials are capable of withstanding the environments encountered when handling exhaust streams, particularly high temperatures.

The substrate may be a highly porous substrate. The term "highly porous substrate" refers to a substrate having a porosity of about 40% to about 80%. A highly porous substrate may preferably have a porosity of at least about 45%, more preferably at least about 50%. A highly porous substrate may preferably have a porosity of less than about 75%, more preferably less than about 70%. The term porosity, as used herein, refers to total porosity, preferably as measured by mercury porosimetry.

Preferably, the substrate may be cordierite, highly porous cordierite, metallic substrate, extruded SCR, wall flow filter, filter or SCRF.

A washcoat comprising a blend of platinum and a first SCR catalyst on a siliceous support can be applied to the inlet side of the substrate using methods known in the art, the first SCR catalyst being preferably a Cu-SCR catalyst or Fe -SCR catalyst. After application of the washcoat, the composition may be dried and calcined. As described above, when the composition includes a second SCR, the second SCR may be applied to the calcined article with an underlayer in a separate washcoat. After the second washcoat is applied, it may be dried and calcined as was done for the first layer.

The substrate having the platinum containing layer may be dried and calcined at a temperature within the range of 300 °C to 1200 °C, preferably 400 °C to 700 °C, and more preferably 450 °C to 650 °C. Calcination is preferably carried out under dry conditions, but can also be carried out by means of hot water, ie in the presence of some moisture content. Calcination may be performed for a time period of about 30 minutes to about 4 hours, preferably about 30 minutes to about 2 hours, more preferably about 30 minutes to about 1 hour.

The exhaust system may include a catalyst having one of the 11 arrangements described above and means for forming NH ₃ in the exhaust gas, wherein the NH ₃ is formed from the exhaust gas prior to contacting the exhaust gas with the catalyst.

The exhaust system comprises (1) a catalyst comprising platinum on a support having low ammonia storage and a first SCR catalyst, the first SCR catalyst being preferably a Cu-SCR catalyst or a Fe-SCR catalyst and the first SCR catalyst being a platinum A catalyst present as a blend with the catalyst and (2) a means for forming NH ₃ in the exhaust gas, wherein the NH ₃ is formed from the exhaust gas prior to contacting the exhaust gas with the catalyst. The exhaust system comprises (1) a catalyst comprising a blend of platinum on a support with low ammonia storage and a first SCR catalyst, wherein the first SCR catalyst is preferably a Cu-SCR catalyst or a Fe-SCR catalyst; (2 ) a second SCR catalyst positioned adjacent to the blend of platinum on a support with low ammonia storage and the first SCR catalyst and at least partially overlapping the blend of platinum on a support with low ammonia storage with the first SCR catalyst, and (3 ) means for forming NH ₃ in the exhaust gas, wherein NH ₃ is formed from the exhaust gas before contacting the exhaust gas with the catalyst. The exhaust system comprises (1) a catalyst comprising a blend of platinum on a support with low ammonia storage and a first SCR catalyst, wherein the first SCR catalyst is preferably a Cu-SCR catalyst or a Fe-SCR catalyst; (2 ) a second SCR catalyst positioned adjacent to the blend of platinum on a support with low ammonia storage and the first SCR catalyst and at least partially overlapping the blend of platinum on a support with low ammonia storage with the first SCR catalyst, (3 ) a third SCR catalyst positioned adjacent to the blend of platinum on a support with low ammonia storage and the first SCR catalyst and at least partially overlapping with the blend of platinum on a support with low ammonia storage and the first SCR catalyst, and ( 4) Means for forming NH ₃ in the exhaust gas may include means in which NH ₃ is formed from the exhaust gas before contacting the exhaust gas with the catalyst.

In another aspect of the invention, a method of improving N ₂ yield from ammonia in an exhaust gas at a temperature of about 250° C. to about 350° C. comprises contacting an exhaust gas containing ammonia with the catalyst of the first aspect of the invention. Include steps. An improvement in yield is obtained from a comparative formulation in which the first SCR catalyst is present as the first layer and the supported platinum is present in the second layer and the gas comprising NH ₃ passes through the first layer before passing through the second layer. from about 10% to about 20% at about 250 °C compared to the included catalyst.

In another aspect of the present invention, a method for improving the N ₂ yield from ammonia in an exhaust gas at a temperature of about 250° C. to about 350° C. is provided by using an exhaust gas comprising ammonia and (1) on a support having low ammonia storage. a blend of platinum and the first SCR catalyst, wherein the first SCR catalyst is preferably a Cu-SCR catalyst or a Fe-SCR catalyst, and the first SCR catalyst is present as a blend with platinum; and (2) low ammonia. contacting a catalyst comprising a second SCR catalyst positioned adjacent to the blend of platinum and first SCR catalyst on a support having a low ammonia storage and at least partially overlapping the blend of platinum and first SCR catalyst on a support having low ammonia storage. It includes steps to An improvement in yield is obtained from a comparative formulation in which the first SCR catalyst is present as the first layer and the supported platinum is present in the second layer and the gas comprising NH ₃ passes through the first layer before passing through the second layer. from about 10% to about 20% at about 250 °C compared to the included catalyst.

In another aspect of the present invention, a method for improving the N ₂ yield from ammonia in an exhaust gas at a temperature of about 250° C. to about 350° C. is provided by using an exhaust gas comprising ammonia and (1) on a support having low ammonia storage. A blend of platinum and the first SCR catalyst, wherein the first SCR catalyst is preferably a Cu-SCR catalyst or a Fe-SCR catalyst, and the first SCR catalyst is present as a blend with platinum; a second SCR catalyst positioned adjacent to the blend of platinum and first SCR catalyst on a support with low ammonia storage and at least partially overlapping the blend of platinum on support with low ammonia storage and the first SCR catalyst; and (3) a low ammonia storage. contacting a catalyst comprising a third SCR catalyst positioned adjacent to the blend of platinum and first SCR catalyst on a support having a low ammonia storage and at least partially overlapping the blend of platinum and first SCR catalyst on a support. includes An improvement in yield is obtained from a comparative formulation in which the first SCR catalyst is present as the first layer and the supported platinum is present in the second layer and the gas comprising NH ₃ passes through the first layer before passing through the second layer. from about 10% to about 20% at about 250 °C compared to the included catalyst.

In another aspect of the present invention, a method for reducing N ₂ O formation from NH ₃ in an exhaust gas comprises a catalyst comprising a blend of an exhaust gas containing ammonia and a first SCR catalyst with platinum on a support having low ammonia storage. and contacting, wherein the first SCR catalyst is preferably a Cu-SCR catalyst or a Fe-SCR catalyst. The decrease in N ₂ O yield is for comparison where the first SCR catalyst is present as the first layer and the supported platinum is present in the second layer and the gas comprising NH ₃ passes through the first layer before passing through the second layer. from about 40% to about 70% at about 250 °C compared to the catalyst comprising formulation.

In another aspect of the present invention, a method for reducing N ₂ O formation from NH ₃ in an exhaust gas comprises a blend of a first SCR catalyst with an exhaust gas comprising ammonia and (1) platinum on a support having low ammonia storage. , the first SCR catalyst, preferably the Cu-SCR catalyst or the Fe-SCR catalyst, is present as a blend with platinum, and (2) adjacent to the blend of platinum and the first SCR catalyst on a support having low ammonia storage. and contacting a catalyst comprising a second SCR catalyst at least partially overlapping the blend of the first SCR catalyst and platinum on a support having low ammonia storage. The decrease in N ₂ O yield is for comparison where the first SCR catalyst is present as the first layer and the supported platinum is present in the second layer and the gas comprising NH ₃ passes through the first layer before passing through the second layer. from about 40% to about 70% at about 250 °C compared to the catalyst comprising formulation.

In another aspect of the present invention, a method for reducing N ₂ O formation from NH ₃ in an exhaust gas comprises a blend of a first SCR catalyst with an exhaust gas comprising ammonia and (1) platinum on a support having low ammonia storage. , a blend, wherein the first SCR catalyst is a Cu-SCR catalyst or a Fe-SCR catalyst, and the first SCR catalyst is present as a blend with platinum, (2) a blend of platinum on a support with low ammonia storage and the first SCR catalyst a second SCR catalyst positioned adjacent to and at least partially overlapping the blend of the platinum on support with low ammonia storage and the first SCR catalyst, and (3) the platinum on support with low ammonia storage and the first SCR catalyst; and contacting a catalyst comprising a third SCR catalyst at least partially overlapping the blend of the first SCR catalyst and platinum on a support having low ammonia storage and positioned adjacent to the blend. The decrease in N ₂ O yield is for comparison where the first SCR catalyst is present as the first layer and the supported platinum is present in the second layer and the gas comprising NH ₃ passes through the first layer before passing through the second layer. from about 40% to about 70% at about 250 °C compared to the catalyst comprising formulation.

The following examples merely illustrate the present invention; Those skilled in the art will recognize many variations that fall within the spirit and scope of the invention.

Example

Example 1 - Bilayer blend of 1 wt % Pt on MFI zeolite (SAR = 2100) with Cu-CHA in the bottom layer and Cu-CHA in the top layer, with the entire length of the Pt bottom layer covered by the Cu-CHA top layer.

A bottom layer comprising a washcoat comprising a blend of Cu-CHA (copper chabazite) with 1 wt% Pt on ZSM-5 (MFI framework with SAR = 2100) was applied to the ceramic substrate. The washcoat was pulled down the substrate using a vacuum. The article was dried and calcined at about 500° C. for about 1 hour. The loadings of Pt, high SAR zeolite and Cu-CHA on the article were 3 g/ft ³ , 0.18 g/in ³ , and 1.8 g/in ³ , respectively.

A top layer comprising a second washcoat comprising Cu-CHA was applied to the substrate coated with the bottom layer, then the washcoat was pulled under the substrate to a distance of about 50% of the length of the substrate using a vacuum. The article was dried and calcined at about 500° C. for about 1 hour. The loading of Cu-CHA in the top layer was 1.8 g/in ³ . The article was cut at appropriate locations along the length of the article to form a new smaller article with 100% of the lower blend layer covered by the upper Cu-CHA layer. This material is Example 1. The arrangement of Example 1 is shown in FIG. 1 .

Example 2 - Bilayer blend of 2 wt% Pt on MFI zeolite (SAR = 2100) with Cu-CHA in the bottom layer and Cu-CHA in the top layer, with the entire length of the Pt bottom layer covered by the Cu-CHA top layer

A bottom layer comprising a washcoat comprising a blend of 2 wt% Pt and Cu-CHA on ZSM-5 (MFI framework with SAR = 2100) was applied to the ceramic substrate, and then the washcoat was vacuumed down to the substrate. Pulled. The article was dried and calcined at about 500° C. for about 1 hour. The loadings of Pt, high SAR zeolite and Cu-CHA on the article were 3 g/ft ³ , 0.09 g/in ³ , and 0.9 g/in ³ , respectively.

A top layer comprising a second washcoat comprising Cu-CHA was applied to the substrate coated with the bottom layer, then the washcoat was pulled under the substrate to a distance of about 50% of the length of the substrate using a vacuum. The article was dried and calcined at about 500° C. for about 1 hour. The loading of Cu-CHA in the top layer was 1.8 g/in ³ . The article was cut at appropriate locations along the length of the article to form a new smaller article with 100% of the lower blend layer covered by the upper Cu-CHA layer. This material is Example 2. The arrangement of Example 2 is shown in FIG. 1 .

Example 3 - Bilayer blend of 2 wt% Pt on amorphous silica with Cu-CHA in the bottom layer and Cu-CHA in the top layer, with the entire length of the Pt bottom layer covered by the Cu-CHA top layer

A bottom layer comprising a washcoat comprising a blend of 2 wt% Pt and Cu-CHA on amorphous silica was applied to the ceramic substrate. After the washcoat was applied to the ceramic substrate, the washcoat was pulled under the substrate using a vacuum. The article was dried and calcined at about 500° C. for about 1 hour. The loadings of Pt, high SAR zeolite and Cu-CHA on the article were 3 g/ft ³ , 0.09 g/in ³ , and 0.9 g/in ³ , respectively.

A second washcoat comprising Cu-CHA was used to apply the top layer to the substrate coated with the bottom layer, then the washcoat was pulled under the substrate to a distance of about 50% of the length of the substrate using a vacuum. The article was dried and calcined at about 500° C. for about 1 hour. The loading of Cu-CHA in the top layer was 1.8 g/in ³ . The article was cut at appropriate locations along the length of the article to form a new smaller article with 100% of the lower blend layer covered by the upper Cu-CHA layer. This material is Example 3. The arrangement of Example 3 is shown in FIG. 1 .

Example 4 - Bilayer blend of 1 wt% Pt on alumina with Cu-CHA in the bottom layer and Cu-CHA in the top layer, with the entire length of the Pt bottom layer covered by Cu-CHA

An underlayer comprising a washcoat comprising a blend of 1 wt% Pt and Cu-CHA on alumina was applied to the ceramic substrate and then the washcoat was pulled under the substrate using a vacuum. The article was dried and calcined at about 500° C. for about 1 hour. The loadings of Pt, high SAR zeolite and Cu-CHA on the article were 3 g/ft ³ , 0.09 g/in ³ , and 0.9 g/in ³ , respectively.

A top layer comprising a second washcoat comprising Cu-CHA was applied to the substrate coated with the bottom layer, then the washcoat was pulled under the substrate to a distance of about 50% of the length of the substrate using a vacuum. The article was dried and calcined at about 500° C. for about 1 hour. The loading of Cu-CHA in the top layer was 1.8 g/in ³ . The article was cut at appropriate locations along the length of the article to form a new smaller article with 100% of the lower blend layer covered by the upper Cu-CHA layer. This material is Example 4. The arrangement of Example 4 is shown in FIG. 1 .

Example 5 - Bilayer blend of 2 wt % Pt on titania with Cu-CHA in the bottom layer and Cu-CHA in the top layer, with the entire length of the Pt bottom layer covered by the Cu-CHA top layer

An underlayer comprising a washcoat comprising a blend of 2 wt% Pt and Cu-CHA on titania was applied to the ceramic substrate and then the washcoat was pulled under the substrate using a vacuum. The article was dried and calcined at about 500° C. for about 1 hour. The loadings of Pt, high SAR zeolite and Cu-CHA on the article were 3 g/ft ³ , 0.09 g/in ³ , and 0.9 g/in ³ , respectively.

A top layer comprising a second washcoat comprising Cu-CHA was applied to the substrate coated with the bottom layer, then the washcoat was pulled under the substrate to a distance of about 50% of the length of the substrate using a vacuum. The article was dried and calcined at about 500° C. for about 1 hour. The loading of Cu-CHA in the top layer was 1.8 g/in ³ . The article was cut at appropriate locations along the length of the article to form a new smaller article with 100% of the lower blend layer covered by the upper Cu-CHA layer. This material is Example 5. The arrangement of Example 5 is shown in FIG. 1 .

Examples 1-5 compare the NH ₃ oxidation activity of fresh catalyst with similar blend batches in the bottom layer and fully covered Cu-CHA top layer, the blends comprising Pt on different support materials: siliceous zeolite, silica, alumina and titania. (Table 1). Examples 1-2 gave the highest NH ₃ oxidation activity at 250° C., with a conversion greater than 80%. In contrast, Examples 3-5 provided substantially lower NH ₃ conversions at 250 °C. These results suggest that Pt on a support with low ammonia storage, such as a siliceous support (eg, zeolite or silica), is required to achieve satisfactory NH ₃ oxidation activity.

Comparison of steady-state NH ₃ oxidation activities of fresh catalysts under 200 ppm NH ₃ , 10 % O ₂ , 4.5 % H ₂ O, 4.5 % CO ₂ , balance N ₂ at SV = ^120,000 h -1 Example 250 ℃ active 450 ℃ active NH ₃ Conversion (%) N ₂ Yield (%) N ₂ O (ppm) NO _x (ppm) NH ₃ Conversion (%) N ₂ Yield (%) N ₂ O (ppm) NO _x (ppm) 1 - fresh 80.2 68.7 11.9 0.2 97.1 95.5 1.1 1.1 2 - Fresh 81.6 70.0 11.8 0.4 97.0 95.2 1.3 1.2 3 - fresh 91.2 74.7 17.1 0.1 98.1 95.7 1.7 1.6 4 - fresh 15.4 13.7 1.7 0.0 96.5 94.8 1.3 1.0 5 - fresh 56.5 48.7 7.9 0.2 98.2 94.2 3.2 2.0

Example 6 - Bilayer blend of 4 wt% Pt on MFI zeolite (SAR = 40) with Cu-CHA in the bottom layer and Cu-CHA in the top layer, with the entire length of the Pt bottom layer covered by the Cu-CHA top layer

A bottom layer comprising a washcoat comprising a blend of 4 wt% Pt and Cu-CHA on ZSM-5 (MFI framework with SAR = 40) was applied to the ceramic substrate, and then the washcoat was vacuumed down to the substrate. Pulled. The article was dried and calcined at about 500° C. for about 1 hour. The loadings of Pt, high SAR zeolite and Cu-CHA on the article were 3 g/ft ³ , 0.045 g/in ³ , and 0.9 g/in ³ , respectively.

A top layer comprising a second washcoat comprising Cu-CHA was applied to the substrate coated with the bottom layer, then the washcoat was pulled under the substrate to a distance of about 50% of the length of the substrate using a vacuum. The article was dried and calcined at about 500° C. for about 1 hour. The loading of Cu-CHA in the top layer was 1.8 g/in ³ . The article was cut at appropriate locations along the length of the article to form a new smaller article with 100% of the lower blend layer covered by the upper Cu-CHA layer. This material is Example 6. The arrangement of Example 6 is shown in FIG. 1 .

Example 7 - Bilayer blend of 4 wt% Pt on MFI zeolite (SAR = 850) with Cu-CHA in the bottom layer and Cu-CHA in the top layer, with the entire length of the Pt bottom layer covered by the Cu-CHA top layer

A bottom layer comprising a washcoat comprising a blend of 4 wt% Pt and Cu-CHA on ZSM-5 (MFI framework with SAR = 850) was applied to the ceramic substrate, and then the washcoat was vacuumed down to the substrate. Pulled. The article was dried and calcined at about 500° C. for about 1 hour. The loadings of Pt, high SAR zeolite and Cu-CHA on the article were 3 g/ft ³ , 0.045 g/in ³ , and 0.9 g/in ³ , respectively.

A top layer comprising a second washcoat comprising Cu-CHA was applied to the substrate coated with the bottom layer, then the washcoat was pulled under the substrate to a distance of about 50% of the length of the substrate using a vacuum. The article was dried and calcined at about 500° C. for about 1 hour. The loading of Cu-CHA in the top layer was 1.8 g/in ³ . The article was cut at appropriate locations along the length of the article to form a new smaller article with 100% of the lower blend layer covered by the upper Cu-CHA layer. This material is Example 7. The arrangement of Example 7 is shown in FIG. 1 .

Example 8 - Bilayer blend of 4 wt% Pt on MFI zeolite (SAR = 2100) with Cu-CHA in the bottom layer and Cu-CHA in the top layer, with the entire length of the Pt bottom layer covered by the Cu-CHA top layer

A bottom layer comprising a washcoat comprising a blend of 4 wt% Pt and Cu-CHA on ZSM-5 (MFI framework with SAR = 2100) was applied to the ceramic substrate, and then the washcoat was vacuumed down to the substrate. Pulled. The article was dried and calcined at about 500° C. for about 1 hour. The loadings of Pt, high SAR zeolite and Cu-CHA on the article were 3 g/ft ³ , 0.045 g/in ³ , and 0.9 g/in ³ , respectively.

A top layer comprising a second washcoat comprising Cu-CHA was applied to the substrate coated with the bottom layer, then the washcoat was pulled under the substrate to a distance of about 50% of the length of the substrate using a vacuum. The article was dried and calcined at about 500° C. for about 1 hour. The loading of Cu-CHA in the top layer was 1.8 g/in ³ . The article was cut at appropriate locations along the length of the article to form a new smaller article with 100% of the lower blend layer covered by the upper Cu-CHA layer. This material is Example 8. The arrangement of Example 8 is shown in FIG. 1 .

Examples 6-8 compare catalysts with a blended bottom layer and a fully covered top layer, the blends comprising Pt supported on zeolites with different SAR values (Table 2). When fresh, all three catalysts of Examples 6-8 gave similar NH ₃ conversions at 250 °C, but N ₂ O production at 250 °C was highest for Example 6 (SAR = 40) and Example 8 (SAR = 40). = 2100). These results suggest that highly siliceous zeolites (eg, those with SAR>1000) are most preferred as Pt supports to achieve low N ₂ O formation and high hydrothermal durability.

Comparison of steady-state NH ₃ oxidation activities of fresh catalysts under 200 ppm NH ₃ , 10 % O ₂ , 4.5 % H ₂ O, 4.5 % CO ₂ , balance N ₂ at SV = ^120,000 h -1 Example 250 ℃ active 450 ℃ active NH ₃ Conversion (%) N ₂ Yield (%) N ₂ O (ppm) NO _x (ppm) NH ₃ Conversion (%) N ₂ Yield (%) N ₂ O (ppm) NO _x (ppm) 6 - fresh 88.0 71.9 17.1 0.0 97.8 96.1 1.3 1.1 7 - fresh 88.7 76.4 13.0 0.0 97.3 95.4 1.4 1.2 8 - fresh 90.2 81.1 9.4 0.0 98.3 96.1 1.6 1.5

Example 9 - Double Layer Formation - Top Layer of Pt and Cu-SCR on Alumina - Comparative Example

A bilayer formation with a Pt and SCR top layer on an alumina bottom layer was used as a comparative example.

An underlayer comprising a washcoat comprising 0.3 wt% Pt on alumina was applied to the ceramic substrate and then the washcoat was pulled under the substrate using a vacuum. The article was dried and calcined at about 500° C. for about 1 hour. The loading of Pt on the article was 3 g/ft ³ .

A top layer comprising a second washcoat comprising Cu-CHA was applied to the substrate coated with the bottom layer and then the washcoat was pulled under the substrate using a vacuum. The article was dried and calcined at about 500° C. for about 1 hour. The loading of Cu-CHA in the top layer was 1.8 g/in ³ . This material is Example 9. An aged sample was prepared by aging the sample of Example 9 at 620° C. for 50 hours in an atmosphere containing 10% H ₂ O. The arrangement of Example 9 is shown in FIG. 8 .

Example 10: Pt on MFI zeolite (SAR = 2100) with Cu-SCR top layer only

A monolayer formation of 0.3 wt% Pt on ZSM-5 (MFI framework with SAR = 2100) was used as a comparative example.

A catalyst article comprising a washcoat slurry comprising 0.3 wt % platinum on ZSM-5 (MFI framework with SAR = 2100) was applied to a ceramic substrate and then the washcoat was pulled down the substrate using a vacuum. The platinum loading on the article was 3 g/ft ³ . After drying the substrate to remove moisture, it was calcined at about 500 °C for about 1 hour. This material is Example 10. An aged sample was prepared by aging the sample of Example 10 at 620° C. for 50 hours in an atmosphere containing 10% H ₂ O. The arrangement of Example 10 is shown in FIG. 8 .

Example 11 - Monolayer Blend of Cu-CHA with 4 wt% Pt on MFI Zeolite (SAR = 2100)

A washcoat comprising a blend of 4 wt% Pt and Cu-CHA on ZSM-5 zeolite (SAR 1500) was prepared. The washcoat was applied to the inlet side of the ceramic substrate and then a vacuum was used to pull the washcoat down the substrate. The article was dried and calcined at about 500° C. for about 1 hour. The loadings of Pt, ZSM-5 and Cu-CHA were 3 g/ft ³ , 0.045 /in ³ , and 0.9 g/in ³ , respectively. This material was Example 11. An aged sample was prepared by aging the sample of Example 11 at 620° C. for 50 hours in an atmosphere containing 10% H ₂ O. The arrangement of Example 11 is shown in FIG. 9 .

Example 12 - Bilayer blend of 4 wt% Pt on MFI zeolite (SAR = 2100) with Cu-CHA in the bottom layer and Cu-CHA in the top layer, with 50% of the Pt bottom layer from the inlet covered by the Cu-CHA top layer

A bilayer formulation comprising a blend of 4 wt% Pt and Cu-CHA on a high SAR zeolite in the bottom layer and a 50% Cu-CHA SCR top layer was prepared as described below.

A bottom layer comprising a washcoat comprising a blend of 4 wt% Pt and Cu-CHA on ZSM-5 (MFI framework with SAR = 2100) was applied to the ceramic substrate, and then the washcoat was pulled under the substrate using a vacuum. Pulled. The article was dried and calcined at about 500° C. for about 1 hour. The loadings of Pt, high SAR zeolite and Cu-CHA on the article were 3 g/ft ³ , 0.045 g/in ³ , and 0.9 g/in ³ , respectively.

A top layer comprising a second washcoat comprising Cu-CHA was applied to the substrate coated with the bottom layer, then the washcoat was pulled under the substrate to a distance of about 50% of the length of the substrate using a vacuum. The article was dried and calcined at about 500° C. for about 1 hour. The loading of Cu-CHA in the top layer was 1.8 g/in ³ . The article was cut at appropriate locations along the length of the article to form a new smaller article from the inlet with 50% of the blend bottom layer covered by the Cu-CHA top layer. This material is Example 12. An aged sample was prepared by aging the sample of Example 12 at 620° C. for 50 hours in an atmosphere containing 10% H ₂ O. The arrangement of Example 12 is shown in FIG. 3 .

Example 13 - Bilayer blend of 4 wt% Pt on MFI zeolite (SAR = 2100) with Cu-CHA in the bottom layer and Cu-CHA in the top layer, with 90% of the Pt bottom layer from the outlet covered by the Cu-CHA top layer

A bottom layer comprising a washcoat comprising a blend of 4 wt% Pt and Cu-CHA on ZSM-5 (MFI framework with SAR = 2100) was applied to the ceramic substrate, and then the washcoat was pulled under the substrate using a vacuum. Pulled. The article was dried and calcined at about 500° C. for about 1 hour. The loadings of Pt, high SAR zeolite and Cu-CHA on the article were 3 g/ft ³ , 0.045 g/in ³ , and 0.9 g/in ³ , respectively.

A top layer comprising a second washcoat comprising Cu-CHA was applied to the substrate coated with the bottom layer and then the washcoat was pulled down using a vacuum to a distance of about 50% of the length of the substrate. The article was dried and calcined at about 500° C. for about 1 hour. The loading of Cu-CHA in the top layer was 1.8 g/in ³ . The article was cut at appropriate locations along the length of the article to form a new, smaller article from the outlet with 90% of the blend bottom layer covered by the Cu-CHA top layer. This material is Example 12. An aged sample was prepared by aging the sample of Example 12 at 620° C. for 50 hours in an atmosphere containing 10% H ₂ O. The arrangement of Example 13 is shown in FIG. 10 .

Stability of fresh catalyst or aged catalyst at 620°C/10%H ₂ O/50 h under 200 ppm NH ₃ , 10 % O ₂ , 4.5 % H ₂ O, 4.5 % CO ₂ , balance N ₂ at SV = 120,000 h ^-1 State NH ₃ oxidation activity Example 250 ℃ active 450 ℃ active NH ₃ Conversion (%) N ₂ Yield (%) N ₂ O (ppm) NO _x (ppm) NH ₃ Conversion (%) N ₂ Yield (%) N ₂ O (ppm) NO _x (ppm) 9 - fresh 89.2 62.3 27.7 0.5 98.4 92.2 2.6 7.8 9 - Aging 91.1 58.4 33.3 4.5 98.1 73.4 3.7 44.1 10 - fresh 89.7 65.7 24.8 0.3 98.3 95.0 1.5 3.8 10 - Aging 88.4 70.1 18.8 0.6 97.5 80.0 2.3 31.8 11 - fresh 96.3 83.6 12.4 1.7 98.8 87.7 2.2 18.8 11 - Aging 85.7 77.2 7.7 2.2 98.6 58.3 3.9 76.1 12 - fresh 95.1 83.7 11.2 1.4 98.7 94.0 1.6 6.7 12 - Aging 90.4 82.3 7.6 1.5 97.9 81.5 2.6 28.8 13 - Aging 81.8 75.2 6.5 0.5 98.2 81.5 3.5 27.9 8 - fresh 90.2 81.1 9.4 0.0 98.3 96.1 1.6 1.5 8 - Aging 80.1 74.8 5.4 0.3 96.3 87.6 2.1 13.8

Table 3; ASC with Pt (Examples 8, 11-13) on a siliceous zeolite with top layer arrangement + Cu-CHA blend bottom layer is compared.

Example 9 vs. Example 10:

Both fresh and aged Examples 9 and 10 gave similar NH ₃ conversions at 250 °C and 450 °C. When fresh, Examples 9 and 10 produced similar amounts of N ₂ O at 250 °C. However, after aging, Example 10 produced about 40% less N ₂ O at 250 °C compared to Example 9. When fresh, Examples 9 and 10 produced similar amounts of NO _x at 450 °C. However, after aging, Example 10 produced about 25% less NO _x at 250 °C compared to Example 9. When fresh, Examples 9 and 10 gave similar N ₂ yields at both 250 °C and 450 °C. However, after aging, Example 10 gave about 20% and 10% higher N ₂ yields compared to Example 9 at 250 °C and 450 °C, respectively.

Example 9 vs. Example 11:

Both fresh and aged Examples 9 and 11 gave similar NH ₃ conversions at 250 °C and 450 °C. At 250 °C, fresh and aged Example 11 produced about 55% less and less than 75% N ₂ O compared to fresh and aged Example 9, respectively. As a result, fresh and aged Example 11 provided about 30% higher and 30% higher N ₂ yields at 250 °C compared to fresh and aged Example 9, respectively. At 450 °C, fresh and aged Example 11 produced about 140% more and 70% more NO _x compared to fresh and aged Example 9, respectively. As a result, fresh and aged Example 11 provided about 5% lower and 20% lower N ₂ yields at 450 °C compared to fresh and aged Example 9, respectively.

Example 9 vs. Example 12:

Both fresh and aged Examples 1 and 12 gave similar NH ₃ conversions at 250 °C and 450 °C. At 250 °C, fresh and aged Example 12 produced about 60% less and less than 75% N ₂ O compared to fresh and aged Example 9, respectively. As a result, fresh and aged Example 12 provided about 30% higher and 40% higher N ₂ yields at 250 °C compared to fresh and aged Example 9, respectively. At 450 °C, fresh and aged Example 12 produced similar amounts and less than 35% NO _x compared to fresh and aged Example 9, respectively. As a result, fresh and aged Example 12 provided similar levels and 10% higher N ₂ yield at 450 °C compared to fresh and aged Example 9, respectively.

Example 9 vs. Example 13:

Aged Example 13 provided less than about 10% NH ₃ conversion at 250 °C and a similar level of NH ₃ conversion at 450 °C compared to aged Example 9. At 250 °C, aged Example 13 produced less than 80% N ₂ O compared to aged Example 9. As a result, aged Example 13 provided about 30% higher N ₂ yield at 250 °C compared to aged Example 9. At 450 °C, aged Example 13 produced about 35% less NO _x compared to aged Example 9. As a result, aged Example 13 gave about 10% higher N ₂ yield at 450 °C compared to aged Example 9.

Example 9 vs. Example 8:

Fresh examples 9 and 8 gave similar NH ₃ conversions at 250 °C and 450 °C. Aged Example 8 provided less than 10% NH ₃ conversion at 250 °C and a similar level of NH ₃ conversion at 450 °C compared to Example 9. At 250 °C, fresh and aged Example 8 produced about 65% less and less than 85% N ₂ O compared to fresh and aged Example 9, respectively. As a result, fresh and aged Example 8 provided approximately 30% higher and 30% higher N ₂ yields at 250 °C compared to fresh and aged Example 9, respectively. At 450 °C, fresh and aged Example 8 produced less than 80% and less than 70% NO _x compared to fresh and aged Example 9, respectively. As a result, fresh and aged Example 8 provided 4% higher and 20% higher N ₂ yields at 450 °C compared to fresh and aged Example 9, respectively.

The foregoing embodiments are intended as examples only; The following claims define the scope of the invention.

Claims (71)

A catalyst comprising a combination of platinum and a first SCR catalyst on a support having low ammonia storage, wherein the support having low ammonia storage is a support storing less than 0.001 mmol NH ₃ per m ³ of support; The catalyst according to claim 1 , wherein the support with low ammonia storage is a siliceous support, and the siliceous support comprises a zeolite having a silica to alumina ratio of ≧500. 2. The catalyst of claim 1, wherein the combination is a blend of platinum on a support with low ammonia storage and the first SCR catalyst. 2. The combination of claim 1, wherein the combination is a bilayer comprising an upper layer comprising the first SCR catalyst and a lower layer comprising platinum on a support having low ammonia storage, the lower layer being located on the substrate or between the lower layer and the substrate. 3 Catalyst characterized in that located on the SCR catalyst. delete 3. The method of claim 2 wherein the ratio of the amount of the first SCR catalyst to the amount of platinum on the support having low ammonia storage ranges from 0:1 to 300:1 or from 3:1 to 300 based on the weight of these components. A catalyst characterized in that it is in the range of :1. The catalyst according to claim 1, wherein the first SCR catalyst is a Cu-SCR catalyst containing copper and molecular sieve or a Fe-SCR catalyst containing iron and molecular sieve. The method of claim 2, wherein the platinum is (a) 0.01-0.3 wt%, (b) 0.03-0.2 wt%, (c) 0.05-0.17 wt%, with respect to the weight of the platinum support + the weight of the platinum + the weight of the first SCR catalyst in the blend %, and (d) 0.07-0.15 wt%. 4. The catalyst of claim 3, wherein the platinum is present at 0.1% to 2%, 0.1% to 1%, or 0.1% to 0.5% by weight relative to the weight of the layer. 3. The method of claim 2, further comprising a second SCR catalyst, the second SCR catalyst comprising a platinum on support having low ammonia storage position adjacent to the blend of the first SCR catalyst and platinum on a support having low ammonia storage. A catalyst characterized in that it at least partially overlaps the blend of the first SCR catalyst. 10. The method of claim 9, further comprising a third SCR catalyst, wherein the third SCR catalyst is positioned adjacent to the blend of the platinum on support having low ammonia storage and the first SCR catalyst and is adjacent to the platinum on support having low ammonia storage. The catalyst of claim 1 , wherein the blend of the first SCR catalyst at least partially overlaps the third SCR catalyst. 2. The method of claim 1 wherein the catalyst is compared wherein the first SCR catalyst is present as a first layer and the supported platinum is present in a second layer and a gas comprising NH ₃ passes through the first layer before passing through the second layer. A catalyst characterized in that it provides an improvement in N ₂ yield from ammonia at a temperature of 250 °C to 350 °C compared to a catalyst comprising a solvent formulation. 8. The method of claim 7 wherein the catalyst is compared wherein the first SCR catalyst is present as the first layer and the supported platinum is present in the second layer and the gas comprising NH ₃ passes through the first layer before passing through the second layer. Provides at least one of (a) an improvement in N ₂ yield from ammonia at a temperature of 350 °C to 450 °C, and (b) a reduction in NOx formation at a temperature of 350 °C to 450 °C as compared to a catalyst comprising a solvent formulation Catalyst characterized in that. 2. The method of claim 1 wherein the catalyst is compared wherein the first SCR catalyst is present as a first layer and the supported platinum is present in a second layer and a gas comprising NH ₃ passes through the first layer before passing through the second layer. A catalyst characterized in that it provides reduced N ₂ O formation from NH ₃ compared to a catalyst comprising a solvent formulation. A method for improving the yield of N ₂ from ammonia in exhaust gas at a temperature of 250 °C to 350 °C, comprising the step of contacting the exhaust gas containing ammonia with the catalyst of claim 1, wherein the improvement of the yield is performed using a first SCR catalyst is present as a first layer, platinum on a support for storing ammonia is present in a second layer, and a catalyst including a comparative formulation in which a gas containing NH ₃ passes through the first layer before passing through the second layer; and compared to 5% to 10%. A method for reducing N ₂ O formation from NH ₃ in an exhaust gas, comprising contacting an exhaust gas containing ammonia with the catalyst of claim 1 , wherein the reduction of N ₂ O formation is performed by a first SCR catalyst in a first layer. 20% compared to a catalyst comprising a comparative formulation in which the platinum on the support is present in the second layer and the gas containing NH ₃ passes through the first layer before passing through the second layer. to 40%. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete

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